(370d) Optimizing Off-Grid Solar Brackish Water Desalination Treatment Designs through Advanced Process Modeling and Pilot Testing

The development of effective brackish water desalination systems for remote applications presents significant challenges in mineral scaling prediction and prevention. Water scarcity and security challenges are global in reach but are particularly acute in Sub-Sahara Africa where many countries have devolved water service provision to local levels, decentralizing local water markets. The situation is particularly dire in rural counties, where an estimated 40% of residents lack reliable water access and two-thirds of new water projects fail within five years. This study describes the successful redesign and pilot testing of the GivePower modular desalination system, a photovoltaic-battery powered off-grid reverse osmosis system operating in remote African locations. The research demonstrates how advanced process modeling combined with comprehensive pilot testing can overcome traditional design limitations and achieve substantial performance improvements.

The original GivePower system operated at only 50% water recovery and required expensive antiscalant chemicals to manage scaling from calcium, magnesium, manganese, and silica in brackish groundwater. Elevated nitrate and fluoride concentrations necessitated high-pressure, high-rejection RO membranes. The autonomous nature of these remote installations, combined with intermittent operation and variable feed water chemistry, created optimization challenges that conventional design approaches struggled to address.

The redesign aimed to achieve greater than 75% water recovery while eliminating antiscalant requirements through external brine recycle and lime softening pretreatment using single-stage RO with Toray seawater membranes. Standard commercial software proved inadequate for integrated system optimization, particularly regarding external recycle integration and accurate scaling prediction. While these tools identified scaling thresholds, they provided limited guidance for design modifications.

We utilized WaterTAP, an advanced open-source water treatment modeling platform developed with U.S. Department of Energy sponsorship. WaterTAP incorporates sophisticated geochemical modeling capabilities that enable accurate scaling assessment for complex water chemistries through integration of external geochemical models, here in using PHREEQC and Reaktoro, providing precise mineral activity coefficient calculations.

Pilot testing revealed critical insights that transformed the design approach. Initial testing identified significant calcite and brucite scaling risks in the original configuration. However, systematic pilot testing demonstrated that strategic pH management could eliminate these scaling issues. Maintaining pH around 11 during lime softening followed by pH reduction prior to RO proved highly effective in preventing mineral precipitation while maintaining treatment efficacy.

The pilot testing program established quantitative relationships between pH adjustment and achievable water recovery, enabling optimization for both cost-effectiveness and performance. These empirical findings validated modeling predictions while revealing operational nuances that modeling alone might overlook. Testing demonstrated that careful pH control achieved target recovery rates without antiscalant addition, representing operational simplification and significant cost reduction.

Field deployment and extended pilot testing confirmed superior performance. The redesigned system consistently achieved recovery rates exceeding 80% while operating reliably in autonomous mode. Antiscalant elimination reduced operational complexity and ongoing costs, critical for sustainable remote operation. The lime softening pretreatment with optimized pH management proved robust across varying feed water conditions.

This research illustrates the critical importance of combining advanced modeling with comprehensive pilot testing for complex water treatment design. The successful GivePower redesign demonstrates that innovative approaches can achieve significant performance improvements while reducing operational complexity and costs, providing a replicable framework for addressing scaling challenges in remote brackish water treatment applications.